In a known functional monitoring method, the monitoring of a load takes place with the aid of so-called transistor monitoring. In this case, it is possible to determine whether the transistor which is used as a switch is "high" or "low" and whether there is a short-circuit of the supply line of the electrical load to the supply voltage or to ground. An interruption in the supply line to the load cannot additionally be detected without an increased circuit cost.
Functional monitoring by means of a switching IC is also known. However, in this method it is not possible to detect which defect is present, that is to say whether there is a short-circuit of the line leading to the load to the supply voltage or to ground, or whether there is a line interruption.
Finally, a method for functional monitoring is also known, in which an intelligent diagnosis IC is used. In this case, it is possible to directly differentiate between the switching states of the switch allocated to the load, a short-circuit of the line leading to the load to the supply voltage or to ground, and a line interruption. However, the cost of defect detection with such monitoring is very high. The information about a defect can be coded, for example via a serial interface, and read out on demand.